Power on reset (POR) circuit is an integral part of a mixed signal device. With the continuous thrust for low power analog circuits, zero power PORs are widely used in mixed signal circuits. Zero power PORs are extremely popular in circuits targeted towards low power consumption. At power up, a digital state machine on an integrated circuit may be in an undefined state. It is important that logic of the digital state machine is in a known state during power up. POR circuits are used to reset the digital state machine at power up, to ensure that the digital state machine starts from a known state.
In addition, during the operation of the integrated circuit, if a power supply to the integrated circuit falls below a certain threshold, a reliable operation of the integrated circuit is jeopardized. This scenario is referred to as a brown out condition. A detector circuit is used to set the threshold and trigger the POR circuit to reset the integrated circuit. This detector circuit also needs to consume zero static power for a zero power solution. Most SoC (system on chip) either do not support the brown out condition with slower ramp rates. Other SoC's burn significant static power to support brown out condition.